Debian Package Management, Part 1: A User's Guide

Debian has one of the most powerful and
versatile package management systems of any Linux distribution. It
is also incredibly cryptic. However, once you start using it, I
promise it does get easier.

Debian's basic package management tool is
dpkg. dpkg is actually built on
top of dpkg-deb, but I'll get into
that later. There are a suite of tools built on top of dpkg,
including dselect,
apt-get,
console-apt and others. This
article functions as a HOWTO, providing commands and instructions
on ways to manipulate dpkg and receive pertinent information about
your Debian, or Debian-based system. I'm not going to cover
everything, but enough so that, you'll be able to use the package
management capabilities of your Debian-based system with
proficiency.

Every Debian package is an archive ending with the extension
“.deb”. For this article, I'll refer to a package as a “deb”.
debs are usually named in the following manner:

zsh_3.1.6.pws21-1.deb

For the examples in this article, I use “foobar.deb” when a
deb needs to be substituted, and “foobar” when a package name is
to be substituted.

For those familiar with the Red Hat Package Management (RPM)
system, dpkg's approach to package management is much different in
its approaches. RPM is a file-based package manager, meaning it
checks for specific files required by a package like
libgtk-1.2.so.0. In contrast, dpkg is package-based, so it checks
to see if you have a specific package, such as libgtk1.2.

Dpkg: The Root of All Debian

Most people will not use dpkg for day-to-day package
management, but it is an incredibly powerful and useful tool.
Dpkg's most basic action is to install a package, which is done
with the command dpkg -i foobar.deb. This will
install the package, while backing up any existing versions of the
package. The command dpkg -i -R /foo/bar will
install all of the debs in a directory.

We all know from experience that sometimes a package won't
install properly or refuses to configure. Or maybe the user aborted
the configure process. dpkg has some helpful tools for making the
configuration process easier. In these instances, dpkg
-configure <package> will finish the configuration
of the specific package, and dpkg --configure
--pending will configure all packages with configuration
pending.

It is just as easy to remove packages with a few simple
commands. Using either dpkg -r <package>
or dpkg -remove <package> will remove a
package and leave its configuration files. If you want to remove
all files related to the package, including its configuration
files, use the command dpkg --purge
<package>.

Getting Information

Debian package management provides several ways to find
information on what packages are currently installed and what files
each package provides. One way to sort packages is by using a
pattern, facilitated with the command dpkg-l
<pattern>. If necessary, a wildcard can be used as
the <pattern>. Using dpkg -l alone will provide a list of all
the packages currently installed on your system.

Using Debian package management also allows you to see what
files were installed by a specific package with the command
dpkg -L <package>. Alternatively, to find
out which package owns a file use dpkg -S
<file>. These searches can also be done with a
pattern, including wildcards.

When you need to get information about a particular deb, this
list of commands is helpful:

In addition to all of the useful information that dpkg
accesses for productive package management, it also has a rich set
of options for screwing up your package management system royally.
To quote dpkg's manpage, “Warning: These options are mostly
intended to be used by experts only. Using them without fully
understanding their effects may break your whole system.” I won't
cover this set of options here, as you should never really need to
use them. However, if you ever need to force dpkg to ignore
dependencies, overwrite files installed by other packages, ignore
conflicts or anything else the Debian package management system is
designed to prevent, look at man dpkg.